1. Field of the Invention
This invention relates to a method and apparatus that uses hydrogen-occluded alloy for recovering power from waste heat, and more particularly to a method and apparatus for recovering power from waste heat that uses hydrogen gas and heat emitted from hydrogen-occluded alloy to drive a turbine to generate power.
2. Description of the Prior Art
There are known hydrogen-occluded alloys such as lanthanum nickel that occlude large quantities of hydrogen. Because small amounts of such alloys are able to occlude large quantities of hydrogen, they are being utilized in various fields of technology.
JP-A-4-295108 discloses an example of a method of generating power by heating a hydrogen-occluded alloy and using the hydrogen gas emitted from the alloy to drive a turbine.
A waste heat recovery power generation apparatus according to the above disclosure uses a two-stage hydrogen-occluded alloy configuration for heat recovery. More specifically, while each alloy stage is connected to a turbine for power generation, there is a difference in the pressure of the hydrogen gas generated at each stage, and as the hydrogen gas is delivered on an alternating basis from one apparatus set, the output varies with time. Moreover, since turbine output decreases relatively for each stage, and since the efficiency of the turbine decreases in proportion to approximately half the square of the output, the output is also affected by the time-based variation, resulting in a decrease in the average output.
Various recovery systems have been proposed in which waste heat is used as the heat source in a low-temperature Rankine cycle that is used to drive the power generation turbine.
However, when this type of conventional low-temperature Rankine cycle system uses a waste heat temperature below about 100.degree. C., the small temperature differential between the heat source and the atmosphere means that the condenser has to be larger, making the overall system relatively large and costly. This results in a higher unit generating cost that makes such systems impractical.
There are examples of hydrogen-occluded alloy based waste heat recovery apparatuses being used as heat pumps or thermal generators. However, owing to the fact that the use of hydrogen-occluded alloy increases the heat capacity of such apparatuses and results in a low efficiency of no more than around 40% of the ideal cycle, such apparatuses have not been applied to power generation or power recovery. A further factor has been the shortcomings of various ideas put forward for achieving high-performance cycles.
An object of the present invention is to provide a method and apparatus for recovering more power from waste heat with iraproved efficiency and low variation in amount of power generated.